The present invention relates to control of compensating impedance connected to supply leading or lagging reactive current to an electric power for stabilization of voltage at a critical bus area, and particularly to a control system responsive to rapid current disturbances.
It is knows that electric power systems which supply highly erratic reactive loads, e.g., electric arc furnaces, are typically characterized by poor voltage regulation. Consequently, these systems often exhibit an undesirable flicker. One system suggested to alleviate this condition is disclosed in U.S. Pat. Nos. 3,936,727 and 3,948,432, respectively issued to Kelley et al. and Kelley, on Feb. 3, 1976 and July 6, 1976. These patents are assigned to the assignee of the present application and are hereby incorporated by reference in the present application.
Generally, the Kelley et al. -- Kelley system includes the use of two control loops: one open compensating control loop; and one closed regulating or supervisory control loop. The compensating control loop senses the reactive load current component and attempts to negate the same by providing the appropriate compensating reactive current component through a reactive converter which includes capacitive and inductive components. The regulating or supervisory control loop employs a current angle sensor to sense the power factor or phase angle at a selected line location which is typically located in a critical area of the line at which good voltage regulation is desired. These two loops cooperate to generally provide a satisfactory degree of voltage regulation when an erratic load is present.
Although the Kelley et al. -- Kelley system is generally satisfactory, its compensating effects are limited by time delays which occur in the sensing of the reactive load current and in the compensating of the sensed reactive load current. More particularly, referring only to the time delay in the "sensing" operation, the reactive load current is sensed two times per cycle of source frequency, i.e., at the zero crossings of the associated projected voltage wavetrain. This twice per cycle sensing of the reactive load current represents an undesirable response time limitation on the Kelley et al. -- Kelley control system, especially in situations where rapid current disturbances occur.
An object of this invention is to provide a more rapidly responsive a-c electric power system in which voltage regulation is provided through reactive load current component sensing.
Another object of this invention is to provide such an electric power system in which the reactive load current component is sensed more than two times per cycle of source frequency.
Another object of this invention is to provide such an electric power system in which the reactive load current component is sensed continuously.
Another object of this invention is to provide an electric power system sensing mechanism for the determination of real or reactive components of current more than two times per cycle of source frequency.